Open AccessReview Bacterial vaginosis and human immunodeficiency virus infection Gregory T Spear*, Elizabeth St John and M Reza Zariffard Address: Department of Immunology/Microbiology,
Trang 1Open Access
Review
Bacterial vaginosis and human immunodeficiency virus infection
Gregory T Spear*, Elizabeth St John and M Reza Zariffard
Address: Department of Immunology/Microbiology, Rush University Medical Center, Chicago, IL 60612 USA
Email: Gregory T Spear* - gspear@rush.edu; Elizabeth St John - Elizabeth_St.John@rush.edu; M
Reza Zariffard - mohammadreza_zariffard@rush.edu
* Corresponding author
Abstract
Epidemiologic studies indicate that bacterial vaginosis (BV), a common alteration of lower genital
tract flora in women, is associated with increased susceptibility to HIV infection Other recent
studies show that HIV is detected more frequently and at higher levels in the lower genital tract of
HIV-seropositive women with BV In vitro studies show that genital tract secretions from women
with BV or flora associated with BV induce HIV expression in infected cells The increased HIV
expression appears to be due at least in part to activation through Toll-like receptors (TLR),
specifically TLR2 Further research is needed to elucidate how BV contributes to HIV acquisition
and transmission
Review
Bacterial vaginosis
Bacteria colonize the lower genital tract of most women
and the predominant species of bacteria in healthy
women is lactobacilli Commonly found vaginal
lactoba-cillus species include Lactobalactoba-cillus crispatus, L gasseri, L.
jensenii and L iners [1,2] Bacterial vaginosis (BV) is
char-acterized by an alteration of genital tract flora such that
the predominant bacteria are no longer lactobacilli, but
instead consist of polymicrobial communities of multiple
genera of gram positive and gram negative organisms [3]
Gardnerella vaginalis, Prevotella sp.,Bacteroides sp.,
Pepto-streptococcus sp., Mycoplasma hominis and Mobiluncus sp as
well as other recently described bacteria are commonly
found in BV [2,3] Lactobacilli, usually L iners, are also
frequently present in BV, but make up a relatively small
proportion of the total flora [2,4] BV has been noted to
be the most prevalent vaginal disorder in adult women
worldwide with the frequency depending on the group
that is studied [5] BV is found in 24% to 37% of women
attending STD clinics but seen at lower rates in women that are not sexually active
BV is associated with an increased risk of infections by HIV and some other organisms as discussed below, as well
as with increased risk of preterm birth, which is a leading cause of infant death in the United States [6-8] Treatment
of BV can reduce preterm birth in high risk cases [7,9] BV
is also associated with miscarriage and pelvic inflamma-tory disease [10-12]
Diagnosis of BV is commonly made by examination of four criteria: vaginal fluid pH (BV results in a pH >4.5); presence of clue cells (bacteria-coated epithelial cells); a homogenous discharge; and production of an amine odor when KOH is added to vaginal fluid [13] Gram stains of vaginal fluid can also aid in diagnosis of BV [14]
Oral or intravaginal antibiotic treatment with metronida-zole or clindamycin cures BV in most women, but BV can resolve spontaneously in nearly a third of subjects
[15-Published: 22 October 2007
AIDS Research and Therapy 2007, 4:25 doi:10.1186/1742-6405-4-25
Received: 3 October 2007 Accepted: 22 October 2007 This article is available from: http://www.aidsrestherapy.com/content/4/1/25
© 2007 Spear et al; licensee BioMed Central Ltd
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Trang 218] However, BV recurs in a significant fraction of treated
women
In vivo studies of the effects of BV on HIV susceptibility and
expression
Several cross-sectional studies performed in Thailand
[19], Uganda [20], and Malawi [21,22] showed that
women with BV had an increased incidence of HIV
infec-tion While suggestive, these studies do not prove a cause
and effect relationship between BV and HIV infection
However, a prospective study in Kenya [23] showed that
the presence of BV and the absence of lactobacilli or
absence of hydrogen peroxide-producing lactobacilli
upon examination were all significantly associated with
acquisition of HIV infection at follow-up
There is also evidence, some of it through cross-sectional
studies, that the presence of BV increases the risk of
infec-tion with several other sexually transmitted infecinfec-tions
(STI), including herpes simplex virus type 2 (HSV-2),
gon-orrhea, Trichomonas vaginalis and Chlamydia trachomatis
[23-25] All of these STI have been suggested to increase
susceptibility of women to sexual transmission of HIV
[26], and so BV may both directly increase HIV
suscepti-bility and indirectly increase it by increasing the number
of women with these other STI
While the above studies suggest that BV can influence
sus-ceptibility of women to HIV infection, other recent studies
suggest that BV increases expression of HIV in the lower
genital tract of women that are already infected with HIV
Thus, the levels of HIV, as assessed by HIV RNA, and the
detection frequency of HIV in the genital tract are
signifi-cantly higher in the genital tract of women with BV when
compared to women without BV [27,28] HIV levels were
inversely correlated with levels of lactobacilli but
posi-tively correlated with Mycoplasma hominis [27] An
addi-tional study showed that women with lower levels of
vaginal lactobacilli had higher genital tract HIV [29]
A number of mechanisms have been suggested that could
account for the increase in susceptibility to HIV and/or
increased expression of HIV in the genital tract (Table 1)
[26,30] These include decreased levels of hydrogen
per-oxide-producing lactobacilli, production by BV flora of
enzymes (e.g mucinases) that degrade protective mecha-nisms such as mucous, or production by BV flora of stim-ulatory substances that increase influx of target cells, HIV expression or infection of cells (see below) In fact, BV is associated with increased levels of pro-inflammatory cytokines such as IL-1β and IL-8 [Reviewed in [31]] IL-1β can induce the production of other pro-inflammatory cytokines, and IL-8 is known to recruit immune cells, thus possibly increasing the number of cellular targets for HIV infection [32]
In vitro studies of the relationship between BV and HIV
A number of in vitro studies show that genital tract fluids from women with BV are highly stimulatory for immune cells and can up-regulate expression of HIV Thus, incuba-tion of the chronically-HIV-infected monocytic cell line U1 with genital fluid from women with BV substantially increased HIV expression [33-36] In contrast, genital fluid collected from women without BV did not induce HIV expression HIV expression was also induced in T cell lines and in peripheral blood mononuclear cells by geni-tal fluids from women with BV [35,37] The substances in genital fluids that stimulated HIV expression in cells were found to function through activation of NF-kB [37] Bacteria from BV have also been tested for their ability to
stimulate HIV expression in cells Gardnerella vaginalis, the
bacterium most frequently isolated in BV, significantly induced HIV expression in U1 cells [38,39] Lysozyme treatment reduced U1 activation suggesting a cell wall
component of G vaginalis was involved in stimulation of the U1 cells Anaerobes Peptostreptococcus asaccharolyticus and Prevotella bivia also stimulated HIV expression [40] as did non-anaerobic bacteria Mycoplasma hominis and Strep-tococcus [39] In contrast, other bacteria found in genital samples including Bacteroides ureolyticus, Peptostreptococcus anaerobius, and Lactobacillus acidophilus did not stimulate
HIV expression [40]
Taken together, many of the above studies suggested that the HIV-stimulatory activity in genital fluids acted through Toll-like receptors (TLR) For example, genital fluids stimulated HIV expression through the NF-kB path-way [41], and stimulation of cells through TLR is well doc-umented to activate NF-kB [42] Also, many of the ligands for TLR are bacterial products [42] and BV mucosal fluids would be expected to contain such products A recent study using the 293 cell line modified to express either TLR2, TLR4 or control cells expressing no functional TLR, directly determined whether mucosal fluids from women with BV stimulated cells through TLR [41] The results showed that genital fluids from women with BV stimu-lated cells predominantly through TLR2, while surpris-ingly there was relatively little stimulation through TLR4
In contrast, fluids from women without BV stimulated
Table 1: Possible mechanisms of bacterial vaginosis effects on
HIV transmission and HIV replication
Increased vaginal pH
Decreased levels of hydrogen peroxide-producing lactobacilli
Production by BV flora of enzymes or substances that inhibit
anti-HIV immunity
Increased influx of cells susceptible to HIV infection
Increased HIV expression and/or infection
Trang 3cells relatively little through either TLR2 or TLR4 Further,
the TLR2-positive cells supported higher levels of
expres-sion of the HIV promoter when exposed to genital
secre-tions from women with BV, suggesting that HIV-infected
cells in the genital tract might express higher levels of HIV
during episodes of BV Other studies showed that genital
tract fluid from women with BV can stimulate
lym-phocytes and other cells to express higher levels of TLR4
and TNF-α [43]
Dendritic cells (DC), cells important for antigen
process-ing and presentation to the immune system, are found in
the lower genital tract and are known to express both
TLR2 and TLR4 DC are suggested to be one of the first
cells that take up HIV during sexual transmission [44,45]
DC are also potent antigen presenting cells whose
func-tion would be important for vaccinafunc-tion against a number
of mucosal pathogens, including HIV We have
investi-gated the hypothesis that genital tract secretions from
women with BV might substantially affect either DC
anti-gen presenting function or DC uptake and infection by
HIV We observed that secretions from women with BV
potently stimulate secretion of IL-12 by monocyte-derived
dendritic (MDDC) (Figure 1) [46] Genital fluid from
women with BV also increased MDDC secretion of IL-23
and p40 and upregulated cell surface HLA-DR, CD40 and
CD83 Further, BV fluids decreased MDDC endocytic abil-ity (a marker of stimulation and maturation of DC) and increased proliferation of T cells in an allogeneic MLR with MDDC as the antigen presenting cells [46] Genital fluids from women without BV had much lower or no stimulatory activity for MDDC These studies suggest that
BV may substantially affect local DC antigen presenting function in women
Since the above studies showed that BV genital secretions potently stimulate DC, we hypothesized that this stimula-tion might increase infecstimula-tion of DC or enhance the ability
of DC to transfer HIV to T cells However, our studies to date do not show BV enhancing HIV infection of DC (Fig 2) or transfer of HIV by DC to T cells (Fig 3) In fact, BV genital secretions appear to suppress HIV transfer to T cells (Fig 3) While our studies currently do not support a role for direct effects of BV genital secretions on DC in enhanc-ing HIV transmission, these findenhanc-ings do not rule out the possibility that BV promotes HIV transmission by altering
DC function or trafficking in vivo
Conclusion
While it has become evident that BV has effects on HIV transmission, HIV genital tract levels and HIV expression
in vitro, further work is needed to identify the mecha-nisms responsible for these effects For example, ques-tions remain regarding the direct contribution of bacterial flora versus indirect mechanisms through immune cells, immune mediators such as cytokines or other mediators
Effect of Bacterial Vaginosis on HIV infection of MDDC
Figure 2
Effect of Bacterial Vaginosis on HIV infection of MDDC MDDC were produced and treated with either Medium alone, BV CVL, Normal CVL or LPS for 48 hr as described in the Figure 1 legend Treated MDDC were incubated with HIV-1Bal for 24 hr DNA was then isolated from the MDDC and analyzed for HIV DNA copies by real time PCR Bars represent mean + standard error
Medium LPS BV Normal AZT 0
100 200 300 400 500
Bacterial Vaginosis induces IL-12p70 production by Dendritic
Cells
Figure 1
Bacterial Vaginosis induces IL-12p70 production by Dendritic
Cells Monocyte-derived dendritic cells (MDDC) were
pro-duced from monocytes isolated from the blood of normal
donors using standard methods [46] MDDC were incubated
for 48 hours with either culture medium alone (Medium),
lipopolysaccharide at 1 µg/ml (LPS), or genital tract
secre-tions collected by cervicalvaginal lavage from women with BV
(BV CVL) or normal flora (Normal CVL) The BV CVL and
Normal CVL were pools of equal amounts of CVL from 15
and 14 women respectively Status of CVL donors was
deter-mined by gram stain Supernatants were harvested and
ana-lyzed for IL-12p70 by ELISA
Medium LPS BV CVL Normal CVL
0
500
1000
1500
2000
2500
Trang 4New in vitro experimental systems or animal models are
needed to help elucidate these mechanisms and are likely
to lead to increased understanding of ways to prevent the
spread of the HIV epidemic
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Effect of Bacterial Vaginosis on HIV transfer from MDDC to
T cells
Figure 3
Effect of Bacterial Vaginosis on HIV transfer from MDDC to
T cells MDDC were produced and treated as described in
the Figure 2 legend and then exposed to HIV-Bal for 2 hours
Free virus was removed by washing and MDDC were
incu-bated with PHA stimulated PBMC Five days later
superna-tants were harvested analyzed for p24 production by ELISA
Bars represent mean + standard error
Medium LPS BV Normal AZT
0
20000
40000
60000
80000
100000
120000
140000
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